This invention relates to microwave devices, and more particularly to RF switched filter circuits.
Microwave switched filter banks are used in some microwave applications, and provide the capability of selectively filtering an input RF signal with a desired filter characteristic. One exemplary filter assembly architecture places the set of band pass filters in one assembly, and positions the input switch circuitry on one side of the filter assembly, and the output switch circuit on the opposite side of the filter assembly, with the RF signals entering and leaving each of the switch circuitry and the filter bank in alignment with a single axis. While this architecture provides relatively high isolation between the input switch circuitry and the output switch circuitry, it is not a compact architecture, and requires additional space or volume.
Another filter assembly architecture places the input switch circuitry and the output switch circuitry on the same side of the band pass filter bank, but with the RF signals entering the input switch circuitry and exiting the output switch circuitry along one axis, which RF signals are passed between the input circuitry and the filter bank, and between the filter bank and the output circuitry, along a second axis orthogonal to the first axis. This alternate architecture is compact, but provides relatively low isolation between the input switch circuitry and the output switch circuitry since both are disposed on the same side of the filter bank.
A multi-channel microwave switched filter bank is described, wherein the input circuitry and output circuitry are mounted on opposite sides of the filter bank, providing a compact structure with excellent isolation.
In a preferred embodiment, the filter bank includes a plurality of microwave band pass filter circuits. A housing structure provides an outer conductive peripheral frame structure. A rack structure has a plurality of elongated slots for mounting therein corresponding ones of the plurality of filter circuits. The rack structure is disposed within the housing structure. A top dielectric substrate board is mounted adjacent a first side of the rack structure and has a first set of openings formed therein for providing access to a first set of input/output (I/O) ports of the plurality of filter circuits. A bottom dielectric substrate board is mounted adjacent a second side of the rack structure opposite the first side and has a second set of openings formed therein for providing access to a second set of input/output (I/O) ports of the plurality of filter circuits. A first switch circuit is mounted to the top dielectric substrate board for selecting one or more filter channels for connection to a first RF transmission line. A second switch circuit is mounted to the bottom dielectric substrate board for selecting one or more filter channels for connection to a second RF transmission line.